We covered dismantling of the engine in the article ‘Dismantling the engine’. There we looked at how to remove the crankshaft. Let us now look at how to dismantle the crankshaft itself and diagnose it.
Before dismantling the crankshaft, it must be washed in petrol and dried.
Inspect the crankshaft.
If it has cracks or severe scoring, the crankshaft cannot be repaired.
We dismantle the crankshaft both for replacement and for boring.
Using a three-legged puller, we press off the drive gear together with the thrust washer.
The thrust washer has a chamfer; on reassembly the washer must be fitted with the chamfer towards the crankshaft counterweight.
With a thin chisel we drive out the gear key.
We remove the thrust washers limiting the axial movement of the crankshaft.
The front washer is held against turning by two pins.
One pin is fitted in the block, the other on the cap of the first main bearing.
We fit the rectangular lug of the rear washer into the slot on the other side of the first main bearing cap.
If the main and big-end journals show minor scores, scratches, scoring, or the journal ovality exceeds 0.01 mm, the journals must be ground to the repair size.
After grinding, the journals must be polished.
The sharp edges of the oilway chamfers are blunted with an abrasive cone.
The repair sizes of the shaft journals are given in the table.
Nominal and maximum permissible dimensions of the mod. 402 engine
| Part name | Nominal diameter, mm | Mating part name | Nominal diameter, mm |
|---|---|---|---|
| Crankshaft | 64.0−0.02 | Main bearing shells | 68.5+0.019 − 2 (2.25−0.01) 68.5+0.019 − 2 (2.25−0.017) |
| 1st repair size 63.75−0.02 |
1st size 68.5+0.019 − 2 (2.375−0.01) 68.5+0.019 − 2 (2.375−0.017) |
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| 2nd repair size 63.5−0.02 |
2nd size 68.5+0.019 − 2 (2.5−0.01) 68.5+0.019 − 2 (2.5−0.017) |
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| 3rd repair size 63.25−0.02 |
3rd size 68.5+0.019 − 2 (2.265−0.01) 68.5+0.019 − 2 (2.265−0.017) |
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| Crankshaft | 58.0−0.02 | Big-end bearing shells | 61.5+0.019 − 2 (1.75−0.005) 61.5+0.019 − 2 (1.75−0.012) |
| 1st repair size 57.75−0.02 |
1st size 61.5+0.019 − 2 (1.875−0.005) 61.5+0.019 − 2 (1.875−0.012) |
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| 2nd repair size 57.5−0.02 |
2nd size 61.5+0.019 − 2 (2.0−0.005) 61.5+0.019 − 2 (2.0−0.012) |
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| 3rd repair size 57.25−0.02 |
3rd repair size 61.5+0.019 − 2 (2.125−0.005) 61.5+0.019 − 2 (2.125−0.012) |
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| Gearbox input shaft nose bearing | 40.0−0.011 | Crankshaft | 40.0−0.012 40.0−0.028 |
| Flywheel | 122.0+0.04 | Crankshaft | 122.0−0.028 |
| Flywheel | 320.0+0.64 320.0+0.54 |
Starter ring gear | 320.0+0.15 |
| Crankshaft | 38.0+0.05 length of the first main journal |
No. 1 main bearing saddle and thrust washers | 33.0−0.05 + 2.5−0.05 + 2.35 ± 0.025 saddle width + washer thickness |
| Crankshaft | 38.0+0.02 38.0+0.003 |
Pulley hub | 38.0+0.007 38.0−0.02 |
| Crankshaft pulley | 57.0+0.06 | Pulley hub | 57.0−0.06 |
| Crankshaft | 40.0+0.027 40.0+0.009 |
Crankshaft gear | 40.0+0.027 |
| Crankshaft | 40.0+0.027 40.0+0.009 |
Thrust washer | 40.0+0.25 40.0+0.08 |
Fits of the mating parts of the crankshaft
| Part name | Clearance, mm | Interference, mm | ||
|---|---|---|---|---|
| min | max | min | max | |
| Crankshaft (nominal) | 0.02 | 0.073 | — | — |
| 1st repair size | 0.02 | 0.073 | — | — |
| 2nd repair size | 0.02 | 0.073 | — | — |
| 3rd repair size | 0.02 | 0.073 | — | — |
| Crankshaft (big-end) | 0.01 | 0.063 | — | — |
| 1st repair size (big-end) | 0.01 | 0.063 | — | — |
| 2nd repair size (big-end) | 0.01 | 0.063 | — | — |
| 3rd repair size (big-end) | 0.01 | 0.063 | — | — |
| Input shaft nose bearing | — | — | 0.001 | 0.028 |
| Flywheel (on journal) | 0 | 0.068 | — | — |
| Flywheel (on ring gear) | — | — | 0.39 | 0.64 |
| Crankshaft (axial) | 0.125 | 0.325 | — | — |
| Crankshaft (pulley hub) | — | 0.04 | — | 0.004 |
| Crankshaft pulley | 0 | 0.12 | — | — |
| Crankshaft (gear) | — | 0.018 | — | 0.027 |
| Crankshaft (thrust washer) | 0.053 | 0.241 | — | — |
After boring, we unscrew the crankshaft oilway plugs.
We wash the oilways with diesel fuel or kerosene and blow them through with compressed air.
We screw in the plugs and tighten them to 38–42 N·m (3.8–4.2 kgf·m).
With a centre punch we stake the edges of the plugs.
After grinding the crankshaft journals, main and big-end bearing shells of the corresponding repair size must be fitted.
Inspect the main bearing shells.
If they show scores, scoring, scratches, flaking, embedded hard particles, etc., replace the shells.
Inspect the flywheel.
If the flywheel ring gear teeth are damaged, or there is scoring, scratching, etc. on the surface mating with the clutch driven plate, replace the flywheel.
If the flywheel has cracks, it must also be replaced.
Inspect the crankshaft oil seal in the timing gear cover.
If the seal is damaged (tears, pull-outs, heavy wear of the working lip, etc.), it must be prised out of the cover with a screwdriver and a new one pressed in.
With high mileage, replacement of the seal is recommended.
Replace the rear crankshaft packing in the main bearing saddle and in the holder.
Remove the old packing and insert a new one about 120 mm long.
Cut the ends of the packing so that it protrudes 0.5–1.0 mm above the plane of the saddle and holder. (Carry out this operation if the engine has a packing; if it has a seal, this operation is not required — the seal must be replaced.)
Compress the packing: to do this, place drift 1 in the bearing saddle, fit holder 4 and the main bearing cap and tighten nuts 3 and bolts 2.
The figure gives the dimensions of the crankshaft packing compression drift.
Replace the rubber seals 1 (flags).
A closed-type input shaft nose bearing is pressed into the crankshaft bore on the flywheel side.
Inspect the bearing; if defects are found (excessive play, sticking, damage to the protective rings, etc.), press it out of the crankshaft with a puller.
Press in a new bearing flush with the lower edge of the chamfer of the crankshaft bore.
